The invention relates to a system for treating fluids, especially water, in a pipe to resist scale deposits from building up in the pipe comprising
a field generating coil mounted exteriorly of the pipe,
an electronic circuit for energising the coil to develop an alternating electromagnetic field in the fluid,
a sensor for sensing a parameter related to the functioning of the system and for generating a parameter dependent signal,
a feed back circuit for feeding back said parameter dependent signal to said electronic circuit to control said circuit.
Systems of this type or known from the prior art. Examples are described in EP0493559, DE19502990, DE19505642
In EP0493559 a system is described wherein the sensor consists of a microphone which is connected in physical contact with the pipe. The microphone picks up any sound that is generated as a result of turbulence inside the pipe. This turbulence relates to the surface effect on water passing through the pipe as well as over obstructions such as limescale deposits. The microphone output signal controls through the feed back circuit the characteristics of the energy supplied to the field generating coil. The supplied energy is related to the flow of water passing through the pipe and to the amount of limescale already build up within the system.
A sensor embodied as an electrode positioned in the wall of the tube and in contact with the fluid is described in DE19502990. The electrode and the thereto connected measuring circuit measures the water velocity. Dependent on the measured velocity the energy supplied to the field generating coil is varied. A disadvantage of this system relies in the fact that the electrode has to be installed inside the pipe, in other words, operations on the pipe have to be performed.
A Similar construction is described in DE19505642. The sensor comprises in this case an elastic electrode carrying a number of strain gauges. Dependent on the velocity of the fluid in the pipe the strain gauge signal varies and therewith the amount of power supplied to the field generating coil varies.
A general problem in all these prior art apparatuses is the calibration of the apparatus once it is installed. The influence of the field generated by the field generating coil is dependent on the induction in the fluid. This induction is dependent on en large number of different factors such as:
electrical properties of the fluid, e.g. the electrical conductivity, the higher the conductivity the lower the induction,
the dimensions and the material of the pipe,
the influence of external fields generated e.g. by nearby electrical apparatuses such as washing machines, dryers, ironing apparatuses, pumps, etc.
Most of these factors are not predictable, or at least not accurate enough.
The aim of the invention is now to provide an apparatus of the above-mentioned type which is embodied such that the influence of all these factors is taken into account.
In agreement with this object the invention now provides an apparatus as defined in the first paragraph of this specification, which is characterised in that
the sensor comprises a field measuring coil mounted exteriorly of said pipe near the field generating coil,
the feed back circuit comprises the electronics which together with said measuring coil acts as a field strength meter.
By measuring the real field developed under practical circumstances information is obtained on the basis of which the electronic circuit for energising the coil to develop an electromagnetic field in the fluid can be adjusted such that even under varying circumstances the proper field strength is generated
The field measuring coil can be positioned at various locations, such as around the field generating coil. This position however has the disadvantage that the configuration within the field generating coil is not identical toe the configuration within the field measuring coil. Therefor it is preferred that the measuring coil is positioned alongside the field generating coil with no or small intermediate distance.
It is preferred to use a feedback circuit in the same manner as in the above described prior art. In other words it is preferred that the electronic circuit for energising the coil comprises an amplifier and a signal generator, whereby the amplification value is adjusted dependent on the signal from the field strength meter.